1. Field of the Invention
The present Invention relates generally to controls and electronic circuitry for use In controlling actuators. More particularly, the present invention relates to body-component actuated controls, such as head controls, that provide ease and precision of speed and positioning of linear or rotary actuators, and to apparatus, such as robotic devices and conveyances for handicapped persons that are controlled or powered by linear or rotary actuators.
2. Description of the Related Art
Control of linear and rotary actuators often includes the requirement that speeds and directions of movement of the actuators be precisely controlled. When steering of a vehicle is controlled by controlling speeds and direction of rotation of motors, and when linear actuators are used in robotics, it is important, not only to control the individual actuators, but also to control relative velocities of the actuators.
Conveyances, or electrically-propelled wheelchairs, provide mobility for a multitude of persons ranging in age from children less than three years old who will never walk, to adults who have been injured in accidents, and to elderly people who have acquired infirmities as they have aged. To these people, their freedom of mobility, and to a large extent their ability to be productive citizens in society, depends upon the mobility afforded by a power wheelchair. Included in this large group of people are some who lack either the use of limb or the motor skills to use the kinds of controls on conventional power wheelchairs.
Typically, power wheelchairs have been propelled by separate electric motors drivingly connected to left and right wheels of the wheelchair.
By controlling both voltage and polarity to the motors, control of forward and reverse speeds, speeds and steering have been controlled. This control of steering includes turns in which the wheelchair pivots around one wheel, and pivot turns in which the wheels rotate in opposite directions at the same speed.
The typical control is an X-Y controller in which a joystick is positioned with respect to X and Y axes to selectively adjust the resistances of two potentiometers or inductive transducers. For those with relatively good motor skills, this type of control has two weaknesses; and for others with poorer motor skills, this type of control is beyond use.
One of the weaknesses of this typical X-Y controller is that, when making a sharp turn in one direction, the controller increases the voltage and the speed of one electric motor up to 41 percent. Thus, at the time when good control dictates a reduced speed, a 41 percent increase in the speed of the motor on the outside of the turn results.
Another weakness is extreme steering sensitivity, making it difficult, even for those with good motor skills, to drive in a straight path and to make minor changes in direction.
These two weakness of X-Y controllers, which are inherent to the geometry of conventional X-Y controllers, In addition to making manual control of a joystick impossible for some handicapped persons, also makes it virtually impossible to provide suitable controls for actuation by other body components, such as controls actuated by inclinations of the human head.
Lautzenhiser, in U.S. Pat. No. 5,129,277, issued Jul. 14, 1992, provides an X-Y controller in which Y axis sensitivity is mechanically selectable, thereby overcoming some of the problems that accompany use of other prior art X-Y controllers. This X-Y controller, when used with the steering sensitivity control apparatus of the present invention, provides superior control of both steering and turning.
Lautzenhiser, in U.S. Pat. No. 5,012,165, issued Apr. 30, 1991, integrates signal variations caused by hand tremors, thereby providing an integrated, or averaged, output. While this prior art patent provides an important advance in the art, it does not achieve the advantages of the present invention.
In the present invention, instead of averaging or integrating the magnitudes of two control signals, differences in the two control signals are reduced as an inverse, nonlinear, and steady-state function of the differences in the two control signals.
That is, speeds and steering are controlled by successive inputs to the first and second transducers. As the first and second transducers are successively positioned to successively different positions, successive differences are produced between the two outputs. Therefore, "difference," as used herein, refers to a single difference in the two outputs that is produced by a single positioning of the transducers. In like manner, referring to "differences" reflects the fact that differences in the outputs are produced by successive positioning of the transducers.
Bell, in U.S. Pat. No. 4,667,136, issued 19 May 1987, teaches placing a resistor between the outputs of two potentiometers to reduce the differences between the two electrical signals and thereby to reduce steering sensitivity.
While Bell's use of a resistor does achieve a decrease steering sensitivity, it is important to notice that the decrease in differences between the electrical signals produced by the two potentiometers is linear. That is, a small difference in electrical signals produces a small decrease in the difference between the electrical signals, and larger differences result in proportionally larger decreases in the differences.
When differences between the electrical signals are small, such as when attempting to steer a straight path, a large percentage decrease in the differences in the electrical signals is needed to effectively reduce steering sensitivity, but Bell's resistor provides a relatively small, and therefore insufficient, reduction in the differences between the two electrical signals unless the resistance of Bell's resistor is relatively small.
However, when attempting to make a sharp turn or a pivot turn, and the differences between the electrical signals are large, a large decrease in the differences in the electrical signals decreases steering sensitivity so severely that it is impossible to effect sharp turns and pivot turns.
Therefore, the use of any fixed resistor having a resistance that adequately reduces sensitivity for steering a straight path, or adjustment of a variable resistor to a resistance that achieves useful reduction in sensitivity for steering a straight path, so severely reduces the difference between the two electrical signs, is, when differences between the signals are large, that it is impossible to make sharp turns or pivot turns.